Television tube



April 19, 1938. K. SCHLESINGE R 2,114,610

TELEVISION TUBE Filed July 21, 1933 7/7Ver7 for:

Patented Apr. 19, 1938 UNITED STA ES PATENT OFFICE Application July 21,

1933, Serial No. 681,466

In Germany July 25, 1932 Claims.

The object of the invention is a method of producing television images of large size with cathode ray tubes.

It has been found that in the attempt to in- 5 crease the size of a television image there is very quickly reached with a given number of lines per image a defined limit, above which the image impression, with a given distance of the eye of the observer, noticeably deteriorates. This moment occurs when due to enlargement of the spacing between the lines this spacing between the lines, with a given width of the recording point, is equal to or greater than the lines themselves.

On the other hand it is undoubtedly known that an increase of size with a given intensity of light and size of image point always encounters the difficulty that the surface brightness of the image decreases. With a given size of image point it is only possible to proceed beyond this stage by increasing the intensity of the image point, which from a technical point of view is a difficult matter.

According to the invention two requirements for large total intensity and good psychological effect with a given number of lines are connected up by means of an adapted dimensioning in such a manner that an optimal total effect is obtained. Briefly the dimensioning consists in that the size of the image point, with constant density of light, i. e., with cathode ray tubes having a constant ray current density per square millimetre, is so selected that the lines are disposed closely together. If 2 lines are present and h. is the height of the usual size, the point accordingly requires to be brought to the size This value may naturally be increased to a slight extent; an over-dimensioning of this kind, however, is not essentially favourable, because assuming the image point is substantially square or circular the maximum sharpness of the contour capable of being obtained is determined by exactly the same size, viz., the spacing of the lines.

The measure according to the invention of employing large points represents for the construction of cathode ray tubes a very pleasant simplification. It has been found that a reduction of the image point with a pre-determined size of the source of emission, for example the cathode (or the intermediate diaphragm), is much more difficult than a simultaneous increase in the size of image point and the total strength of the ray current. by means of a given electron-optical system is in proportion to the surface of the cathode.

The size of the image point produced Large points with high density of ray current may be produced in particularly simple fashion by the use of indirectly heated large-surface cathodes. According to the invention there are employed for this purpose more particularly indirectly heated cathodes, the emissive surface of which possesses the form of a cup, preferably open towards the tube space, of a suitable and preferably not excessive diameter. The cup, for example, may have a diameter of 1-5 millimetres, and be connected with a, say, loop-like heating element, possibly by welding. When using television tubes having good developed electron-optical systems (for example, according to the United States Patent No. 2,049,781), which enable the emissive surface to be reproduced on the screen, it is possible in simple fashion to provide the point with a suitable form. Thus, for example, it is possible in accordance with the invention to furnish the cup cathode with a rectangular emissive surface (the greatest expanse of which may conveniently be disposed vertically to the direction of the line), and in this manner to obtain image points of rectangular form, which have been found to be particularly favourable for the method according to the invention.

The invention will be more fully understood from the appended drawing, whereof Fig. 1 shows a Braun tube furnished with a cathode according to the invention, while in Fig. 2 an embodiment of the cathode is shown H on a larger scale, and

Fig. 3 shows a line-screen according to the invention.

In the drawing l is the bulb of the cathode ray tube, 2 a Wehnelt-cylinder, 3 the cathode, 4, 5 and 6 elements of the electron-optical system, I and 8 deflecting means and 9 the fluorescent screen.

In Fig. 2, 3 is the cathode body, [0 the heating filament, l I the preferably rectangular emissive body, arranged in a recess of the cathode body; I2 is the preferably earthed heating line.

As is shown in Fig. 3, the width of each of the lines I4 is equal to 2 being the number of the lines. It is self understood, that practically no separating lines are to be seen in the image.

It is particularly convenient to determine once and for all for a, particular tube the form and size of the image by corresponding selection of the cathode (or an intermediate diaphragm to be reproduced on the screen in place of the cathode) and to dimension accordingly the means determining the dimensions of the optical screen, so that the total arrangement is adjusted to a size of image, which may be varied only within very narrow limits.

Naturally, however, it is also possible to vary the size of the image point in other fashion, and

to alter the strength of the ray current accordingly, so that the tube supplies image points of different size but constant or practically constant surface intensity. Tubes of this nature may readily be employed for the production of images of desired size. The adjustment of the size of the image point may be performed--particularly in the case of high-vacuum tubes-by suitable adjustment of the electron-optical system (displacement of the focal point in such fashion that the same falls in front of or behind the image screen). The adjustment of the strength of the ray current may be efiected, for example, by the application of a suitable constant grid bias to the intensity control grid of the tube.

The formation and dimensioning of the image point in accordance with the invention is of particular importance in connection with a size of image of more than approximately 3 x 4 cm. By using the method according to the invention it is possible, even when employing relatively small numbers of image points, to produce images of large size, which have a considerable strength of light and are well recognizable even at a considerable distance without auxiliary measures of any kind, such as projection or the like, and reveal the maximum sharpness of image which is capable of being obtained with the particular number of image points concerned.

. I claim:

1. A high vacuum electron discharge tube comprising a thermionic cathode, a control electrode surrounding said cathode for controlling the intensity of the electron emission from said cathode, an image receiving screen, an electrostatical electron-optical system acting on the lines of an optical lens, said electron-optical system being arranged between said cathode and said screen, an electrode having an opening of non-circular shape interposed between said cathode and said electron-optical system, said electron-optical system reproducing on said screen said non-circular opening for producing an image point, and means for deflecting said image point in two directions perpendicular to each other for scanning said screen.

2. A high vacuum electron discharge tube comrising an electron emissive area having the shape of the light spot to be reproduced, means to control the intensity of the electron emission from said area, a picture receiving screen, deflecting means ior producing on said picture receiving screen a line screen having the height of h units and comprising z lines, said deflecting means comprising means to deflect the cathode ray in regular periods in the direction in which the height of the line screen is taken, said deflecting means further comprising means to deflect the cathode ray in periods of 2/2 the length of the first mentioned periods in a direction perpendicular to the first mentioned direction, and an electron optical system acting on the lines of an optical lens for reproducing said area on said fluorescent screen for producing a light spot having a height of h/z units taken in the same direction in which the height of the line screen is taken.

3. A high vacuum electron discharge tube comprising an indirectly heated cathode furnished with an emissive area having the shape of the light spot to be reproduced, means to control the intensity of the electron emission from said area, a picture receiving screen, deflecting means for producing on said picture receiving screen a line screen having the height of h units and comprising 2 lines, said deflecting means com.- prising means to deflect the cathode ray in regular periods in the direction in which the height of the line screen is taken, said deflecting means further comprising means to deflect the cathode ray in periods of 1/2 the length of the first mentioned periods in a direction perpendicular to the first mentioned direction, and an electron optical system acting on the. lines of an optical lens for reproducing said area on said fluorescent screen sfor producing a light spot having a height of 11/2 units taken in the same direction in which the height of the line screen is taken.

4. In a cathode ray tube more particularly for television purposes comprising a picture receiving screen: the combination comprising an indirectly heated cathode having in its surface facing said picture receiving surface a recess and an emissive substance in said recess, and means for electron-optically reproducing the area of said electron emissive substance on said picture receiving surface. 7

5. In a cathode ray tube more particularly for television purposes comprising a picture receiving screen: the combination comprising an indirectly heated cathode having in its surface at the side thereof facing said picture receivingsur face a recess and anelectron-emissive substance in said recess, the area of said emissive substance being of non-circular shape, and means electron-optically reproducing the area of said electron emissive substance on said picture receiving surface to produce a non-circular image spot on said picture receiving surface.

KURT SCHLESINGER. 

